The present invention relates to apparatus and methods for accurately depositing radioactive seeds into a patient""s prostate in the vicinity of the patient""s bladder.
The American Cancer Society estimates that over 198,000 new cases of prostate cancer will be diagnosed in the United States in the year 2001 and nearly 31,500 men will die. Excluding non-melanoma skin cancers, prostate cancer is the most common cancer afflicting men in the United States.
Prostate cancer is defined as malignant tumor growth within the prostate gland. A staging system is a standardized way in which the extent to which a cancer is spread is described. The most commonly used system in the United States is called the TNM System of the American Joint Committee on Cancer. The TNM system describes the extent of the primary tumor (T), the absence or presence of metastasis to nearby lymph node (N), and the absence or presence of distant metastasis. (M).
There are four categories for describing the prostate cancer""s T stage. In Stage T1, the tumor is not palpable but is detectable through prostate biopsy or prostatectomy specimen. In Stage T2, the cancer is palpable and is confined to the prostate. In Stage T3, the tumor extends locally beyond the prostate to the connective tissue next to the prostate and/or to the seminal vesicles, but does not involve any other organs. In Stage T4, the cancer has metastacized to the tissues next to the prostate such as the bladder""s external sphincter, the rectum and/or the wall of the pelvis.
There are two N stages. Stage N0 indicates that the cancer has not spread to any lymph nodes. Stage N1 indicates the cancer has metastasized to one or more regional lymph nodes in the pelvis.
Finally, there are two M stages, M0 and M1. Stage M0 indicates that the cancer has not metastasized beyond the regional nodes. In comparison, Stage M1 means that metastases are present in distant (outside the pelvis) lymph nodes, in bones or other distant organs such as lungs, liver or brain.
In the early stages, prostate cancer is most commonly treated by either prostate removal or by brachytherapy. More advanced cases are treated by hormonal manipulation or orchiectomy to reduce testosterone levels and curb spreading of the disease, by chemotherapy, or by external beam radiation therapy.
With regard to treatment of early stage prostate cancer, the state of the art has several drawbacks. Radical prostatectomy is often recommended for treatment of localized stage A and B prostate cancers. Under general or spinal anesthesia, an incision is made through a patient""s abdomen or perineal area, and the diseased prostate is removed. The procedure is lengthy, especially if a lymph node dissection is simultaneously performed, and requires a hospital stay of 2-5 days. Possible complications include impotence and urinary incontinence.
Internal radiation therapy or brachytherapy has recently been developed and holds great promise for the treatment of early stage prostate cancer. Radioactive pellets or seeds of, for example, iodine-125, palladium-103, or iridium-192, are deposited directly into the prostate through needle placement. U.S. Pat. No. 5,928,130 to Schmidt provides a slightly modified example of such a needle device.
Imaging techniques, such as transrectal ultrasound, CT scans, or MRI, are used to accurately guide placement of the radioactive material. Advantageously, radiation from the brachytherapy seeds is administered directly to the prostate with less damage to surrounding tissues, delivering a substantially higher radiation dosage to the prostate than to the surrounding tissues, as compared to external beam radiation therapy. The procedure need only be performed once, and impotence and urinary incontinence complications are significantly reduced, as compared to prostate removal procedures.
The seeds, which are permanently implanted, give off radiation for weeks or months. Their presence causes little discomfort, and they remain in the prostate after decay of the radioactivity. For several weeks following needle insertion, patients may experience pain in the perineal area, and urine may have a red-brown discoloration.
Although, when performed correctly, brachytherapy may provide several benefits when compared to prostate removal and other techniques, current apparatus and methods for delivering the seeds to target locations within the prostate are sub-optimal and are subject to practitioner error. Current methods of identifying the depth of needle insertion are ultrasound imaging or fluoroscopy. The junction of the base of the prostate and the bladder provides a common reference plane for needle insertion. Identifying this critical reference xe2x80x9cbasexe2x80x9d plane is critical to proper needle and seed placement.
A previously known technique for imaging the base plane is to visualize the plane in either transverse or sagittal ultrasound imaging. Injection of contrast agent may facilitate imaging. A catheter, such as a standard Foley catheter, may be inserted into the patient""s urethra proximal of the junction. Contrast agent comprising aerated K-Y jelly and water, may then be injected through an end port of the catheter. The agent moves distally towards the patient""s bladder and is visible to an ultrasound probe, positioned in the patient""s rectum, thereby facilitating imaging. However, bone structure and muscle may obstruct the image making accurate detection of tissue boundaries difficult. In the absence of reliable positional data, however, radioactive seeds may be inadvertently deposited into the patient""s bladder rather than the distal region of the prostate.
Attempts have been made to improve Foley catheters, as well as to facilitate improved imaging within a body lumen. For example, U.S. Pat. No. 5,715,825 to Crowley provides an acoustic imaging catheter with an inflatable dilation balloon and an ultrasound transducer. However, while Crowley may provide improved imaging, the device is mechanically and electrically complex, and is therefore costly.
U.S. Pat. No. 5,916,153 to Rhea, Jr. provides a multifunction, modified Foley catheter. The device described in that patent, however, does not solve needle placement limitations present in previously known devices and methods.
In view of the drawbacks associated with previously-known methods and apparatus for radioactive seed placement, it would be desirable to provide methods and apparatus that accurately detect tissue boundaries.
It further would be desirable to provide methods and apparatus that provide reliable detection of the bladder/prostate tissue boundary.
It also would be desirable to provide methods and apparatus that may be used in conjunction with a standard brachytherapy apparatus.
In view of the foregoing, it is an object of the present invention to provide methods and apparatus that provide reliable detection of the prostate/bladder tissue boundary.
It is also an object of the present invention to provide methods and apparatus that may be used in conjunction with standard brachytherapy.
In accordance with the principles of the present invention, apparatus and methods are provided comprising an elongated needle and means for detecting the boundary between the prostate and the bladder. The needle includes two conductive traces each having a tip region at the distal end of the needle, and a lumen adapted to receive a column of radioactive seeds for deposition into the prostate once the distal end of the needle is properly positioned.
Impedance measurement circuitry coupled to the tip region of the conductive traces of the needle detects whether the distal end of the needle extends into the bladder or is disposed fully within the distal portion of the prostate. Once the distal end of the elongated needle penetrates into the mucosal lining of the bladder, the impedance of the tissue or fluid between the conductive traces decreases due to the change in tissue or the presence of fluid in the bladder. In particular, if the needle penetrates the mucosal lining into the bladder, the presence of electrolytes in urine within the bladder results in a rapid decrease in the measured impedance. Thus, the tissue boundary between the prostate and the bladder may be readily detected. The distal end of the needle then may be withdrawn back into the prostate for deposition of the radioactive seeds within the prostate. Thus, the present invention provides an improved method for detecting the tissue boundary between the prostate and the bladder for use in prostate brachytherapy treatment.